It is known to make reinforcing nonwoven mats from fibers and to use these mats as substrates in the manufacture of a large number of products including structural panels, see U.S. Pat. No. 5,547,743. Methods of making nonwoven mats are also known, such as conventional wet laid processes described in U.S. Pat. Nos. 4,112,174, 4,681,802 and 4,810,576, the disclosures of which are hereby incorporated herein by reference. In these processes a slurry of glass fiber is made by adding fiber to a typical white water in a pulper to disperse the fiber in the white water forming a slurry having a fiber concentration of about 0.2-1.0 weight %, metering the slurry into a flow of white water to dilute the fiber concentration to 0.1 or below, and depositing this mixture on to a moving screen forming wire to dewater and form a wet nonwoven fibrous mat.
This wet nonwoven web of fiber is then transferred to a second moving screen in-line with the forming screen and run through a binder application saturating station where an aqueous binder mixture, such as an aqueous urea formaldehyde (UF) resin based binder mixture, is applied to the mat in any one of several known ways. The binder-saturated mat is then run over a suction section while still on the moving screen to remove excess binder. The wet mat is then transferred to a wire mesh moving belt and run through an oven to dry the wet mat and to cure (polymerize) the UF based resin binder which bonds the fibers together in the mat. Preferably, the aqueous binder solution is applied using a curtain coater or a dip and squeeze applicator, but other methods of application such as spraying are also known.
In the drying and curing oven the mat is subjected to temperatures up to 450 or 500 degrees F. or higher for periods usually not exceeding 1-2 minutes and as little as a few seconds. Alternative forming methods for nonwoven fiber mats include the use of well known processes of cylinder forming, continuous strand mat forming which lays continuous strands of glass fibers in overlapping swirls, and “dry laying” using carding or random fiber distribution.
UF resins, usually modified with one or more of acrylic, styrene butadiene, or vinyl acetate resins, are most commonly used as a binder for glass fiber mats because of their suitability for the applications and their relatively low cost. Melamine formaldehyde resins are sometimes used for higher temperature and/or chemical resistant applications. To improve the toughness of the mats, a combination of higher mat tear strength and mat flexibility, which is needed to permit higher processing speeds on roofing product manufacturing lines and for maximum roofing product performance on the roofs and in other applications, it is common to modify or plasticize the UF resins as described above. The binder content of these finished mats typically are in the range of 15 to 25 weight percent or higher, based on the dry weight of the mat. It is also known to use other types of aqueous latex binders like acrylics, polyester, polyvinyl acetate, polyvinyl alcohol and other types of resinous binders alone or in combination.
Nonwoven fibrous mats are sometimes used as facers for glass fiber insulation blanket and for pressed glass fiber insulation boards and duct liner, the glass fibers in the insulation being bonded together with a binder, typically phenolic resin, that when cured has a yellow, pink, or tan color. Often it is desirable that the mat facer hide the yellow, or other color of the cured insulation substrate, presenting a white surface, but normal glass fiber mat does not cover up the color to the desired extent due to the light transmission of the 10-16 glass fibers normally used in the mat. It is possible to increase the hiding power by adding small diameter glass microfibers, having average diameters of about 2 microns or less, to the mat but this adds considerable cost to the mat, makes the mat weaker and fuzzier and increases the amount of scrap when making this mat due to wrinkling problems.
It is also known, as illustrated by U.S. Pat. No. 5,965,257 to make a mat having zero bleed through when used as a facer mat in the manufacture of foam insulation by heavily coating a dry, bonded mat on a separate coating line. This patent teaches a coating composition comprising one or more fillers and a binder like acrylic latex. It is also known to use off-line coating to make mats having good hiding properties, but off line coating is expensive, often producing a mat that is not cost competitive with alternative facers like kraft fiber papers and plastic films. Although glass fiber, and sometimes polymer fiber, nonwoven mats are superior in other aspects such as durability, thermal and humidity stability, they often loose out to the lower cost alternatives.
It is also disclosed in U.S. Pat. No. 5,001,005 and U.S. Pat. No. 5,965,257 to make a glass fiber mat containing 60-90 weight percent glass fibers 10-40 percent of non-glass filler material and 1-30 percent of a non-asphaltic binder to use as a facer for foam boards. The filler materials are bonded to the glass fibers with the binder and prevent bleed through of the foam precursor materials when the latter is placed in contact with the mat prior to blowing.